Making electrical contact to semiconductor regions such as, e.g., source, drain, and gate regions of a field-effect transistor typically involves the deposition of a metallization over a dielectric which has been patterned to produce openings (windows, holes, vias) to the underlying semiconductor structure. While, currently, aluminum is the material most widely used for semiconductor device metallization, other materials such as, e.g., tungsten and cobalt are also receiving attention. And, primarily in the interest of reduced contact resistance, contact structures have been proposed including one or more additional layers intermediate to metallization and semiconductor materials: for example, in the case of source and drain regions in silicon devices, a layer of titanium silicide is advantageously included between the silicon semiconductor and aluminum metallization materials.
Contact structures and methods for their fabrication have evolved as motivated by a variety of concerns relating not only to contact resistance, but also to step coverage, to electromigration, and to interdiffusion. The following background art is considered as representative in addressing such concerns:
U.S. Pat. No. 4,107,726, issued Aug. 15, 1978 to H. Schilling, discloses metallizations in which aluminum overlies a thin layer of titanium which, in turn, overlies a layer of platinum silicide in contact windows;
U.S. Pat. No. 4,361,599, issued Nov. 30, 1982 to R. L. Wourms discloses a plasma-etching process for making contact openings in a dielectric material, underlying silicide regions serving to inhibit over-etching;
U.S. Pat. No. 4,398,335, issued Aug. 16, 1983 to W. I. Lehrer discloses a silicide metallization which is made by depositing silicon on a dielectric, followed by depositing of a silicide-forming material;
U.S. Pat. No. 4,502,209, issued Mar. 5, 1985 to M. E. Eizenberg et al. discloses exemplary contact structures comprising layers of aluminum, titanium carbide, and titanium silicide on silicon, as well as other, similar multilayer metallization structures.
Quite generally, desirable contact structures in semiconductor integrated-circuit devices have low contact resistance, good step coverage, and protection against interdiffusion and electromigration. In the following, with such desiderata in mind, attention is directed to a contact structure comprising a silicide layer and a metallization layer, and especially to the interface between such layers.